Every cell surfaces of the higher animals are treated with carbohydrates. It has been regarded so far that the role of those carbohydrates is just to protect cell surfaces. However, recent studies have clarified that the structures of those carbohydrates are cell-specific and those carbohydrates play a very important role in recognition between cells (Lis, H. and Sharon, N., Chem. Rev., 1998, 98, 637–674).
Transmitting signals by recognition between cells is highly important to keep an individual stable. Especially, the defense mechanism of human is under the control of recognition between immune cells. Studies have been reported that inflammation, one of human defense mechanism, is caused by specific carbohydrates on cell surfaces and peptides recognizing thereof. Besides, recognition between cells mediated by specific carbohydrates is proven to be essential for metastasis process of cancer, which leads cancer to be a very difficult fatal disease (Fukushima, K., et al., Cancer Res., 1984, 44, 5279–5285; Hanski, C., et al., Cancer Res., 1995, 55, 9280933; Ura, H., et al., World J. Surg., 1997, 21, 773–776).
Though it is not easy to find out the structures of specific carbohydrates on cell surfaces biologically or chemically, it has been successfully found out that one of the carbohydrates specific to cancer cells is sialyl Lewis X (sLeX), an oligosaccharide connected with 4 pyranosides and sLeX along with selectin, a carbohydrate-specific peptide, leads binding between cells (Bertozzi, C. R., Chem. Biol., 1995, 2, 703–708; Lasky, L. A., Science, 1992, 266, 964–968).
The binding power between carbohydrates and selectin is weak at the level of millimolar, but the next joining with integrin, a kind of peptide, produces a strong binding power at the level of micromolar or submicromolar, which is enough power to induce binding and recognition between cells. Since binding and recognition between cells start with recognition between peptides, preparing a subject which controls such recognition can be a basic step for the treatment of diseases caused by recognition between cells.
Studies have been made so far to produce a subject, which can recognize carbohydrates on cell surfaces, but it is still difficult to prepare strong neutralizing molecules. The reason is firstly that carbohydrates have a structure moving freely. Particularly, the hexagon ring of pyranoside can be transformed to a totally different conformation by ring flip and those hexagonal carbohydrates are bound each other with glycosidic bond (C—O—C), which makes it possible to have various different structures. Secondly, it is difficult to recognize carbohydrate molecules because those molecules consist of monosaccharides having similar structures each other. Thirdly, it is very difficult to prepare a carbohydrate-specific antibody since carbohydrate molecules are self-molecules, which hardly evoke antigen-antibody reaction by immune system.
Those reasons are holding scientists not to make a progress of their studies on neutralizing molecules of carbohydrates though carbohydrates are very important target molecules for cell recognition. As a matter of fact, the intensity of binding power of joining or neutralizing molecules is still at low level of mM.
To solve the above problems, the present inventors have developed joining molecules, which can recognize sialyl Lewis X and be bound multiply. Precisely, the present inventors have found peptides, which can bind specifically with sialyl Lewis X using phage display method and prepared those peptides possible for multiple binding in order to increase their low affinity. As a result, peptides, which are bound with specific sialyl Lewis X of the present invention, are confirmed to be joining molecules having a strong affinity under micromol. On the basis of the point that those peptides can recognize carbohydrates specifically connected to cancer cell surfaces, the present inventors have accomplished the present invention by confirming that those peptides can be used for the treatment of diseases mediated by recognition between cells owing to their ability to shut off the recognition between cells mediated by specific carbohydrates and also can be used as a carbohydrate-specific peptides for diagnostic kit, which can diagnoses by confirming the existence of any specific carbohydrate.